Wrong. Read the Didache and the letters of Ignatius of Antioch (who knew your "Rabbi Sha'ul" in the flesh). Christians switched their Sabbath observance to Sunday before the years had three digits.
Have fun with that one!
And Rabbi Sha'ul (What Yeshua called him on the road to Damascus) outlined this in Hebrews 11.
What? No chapter and verse on The LORD's Day??
You are correct. But in a very real sense it doesn't matter anyway, because God asked for "a" Sabbath Day, a day of rest after six work days, and not any specific calendar day, Leviticus 23:3).
Christ endowed the Church with the authority to declare disciplines, such as which day the sabbath shall be, (Mathew 16:19). In any case, what better day to celebrate the Sabbath than the very day that Christ rose from the dead? It is the most important day that humanity could ever know.